An animal bio-assay capable of evaluating the potency of airborne sensory irritants (gases or aerosols) is used to evaluate the cumulative effects of toluene diisocyanate and a variety of di- or monoisocyanates to elucidate the mechanism of such cumulative effects. Benzoquinone, styrene, and styrene oxide will also be used. From the results, predictions for safe levels of exposure are made for each chemical and evaluation of the effect of these levels is done using sister chromatid exchange frequencies in alveolar macrophages after several days of exposures.